1. Field of the Invention
The present invention generally relates to personal communication systems. More specifically, the present invention relates to a system and method for optimizing the forward power control in a personal communication services (PCS) code division multiple access (CDMA) system.
2. Description of the Related Art
A PCS CDMA system checks the generation of a xe2x80x9cforward frame errorxe2x80x9d per frame and carries an erasure indicator bit (EIB) in a reverse frame, in support of forward power control. Parameters associated with PCS forward power control include: Bigup_delta, smallup_delta, down_delta, down_frame_count, max_tx_gain, min_tx_gain, normal_gain, etc.
Tracking error is considered an evaluation criterion for forward power control performance, defined as a difference between the ratio of signal energy per bit to noise energy,       E    b    /      N    o  
measured at a mobile station and the       E    b    /      N    o  
required to maintain a 1% frame error rate.
For an 800 MHz digital cellular CDMA system, forward power control optimization is performed as a live field test. The process can generally be divided into three steps: 1) preparation; 2) field testing; and 3) optimization, each of which are defined below.
A. Preparation
To prepare for live field testing of forward power control performance in accordance with the prior art, a test van which simulates a mobile diagnostic monitor (MDM) and a global positioning system (GPS) for forward link data logging, and a notebook PC for data collection platform (DCP) logging are required.
Furthermore, a test telephone, a zip drive for data backup and a switched virtual connection (SVC) option 9 are required. In addition, eight combinations of forward power control parameters are constructed for analysis.
B. Live Field Testing
Live field testing of forward power control performance comprises the steps of:
1. Checking a receive/transmit path of a system and confirming that there are no faults, i.e., the path operation is normal (step 1);
2. Setting parameter values for the first of eight pre-determined parameter combinations (case 1) at a base station manager (BSM) (step 2); and
3. Logging data associated with service areas of a base transceiver station (BTS) along a determined route using a test van with a data collection platform (DCP) and a mobile diagnostic monitor (MDM) (step 3).
A CDMA analysis tool analyzes the forward power control performance by calculating the forward and reverse average frame error rate. In addition, the average traffic channel digital gain, average       E    C    /      I    O  
and average RX_PWR are calculated.
C. Optimization
Optimizing forward power control in accordance with the prior art includes the steps of:
1. Repeating steps 1 and 2 of part B for all eight parameter combinations.
2. Calculating an average forward frame error rate, average reverse frame error rate and average digital gain for all eight cases.
3. Calculating the average       E    C    /      I    O  
xe2x80x83and Rxxe2x80x94Pwr of each calculated result of step 2.
4. Finding an optimal forward parameter from the measured data for all eight cases. To do so, five values are measured (a forward frame error rate, a reverse frame error rate, an average digital gain, an average Ec/Io and RX_PWR) for eight different parameter combinations. A parameter combination is selected having the best measured values for forward power control.
Since a forward power control algorithm in a PCS system is different from a conventional 800 MHz band digital cellular CDMA system, the method of optimization must be different.
Furthermore, the optimization method described for forward power control is problematic in that it is impossible to duplicate the identical radio environment for each of the eight parameter combinations, since testing is performed in a real field setting.
As a result, a CDMA forward power control technique based on IS-95 was developed. An object of this technique is to minimize interference on neighboring cells by differentiating power allocation in accordance with the state of each subscriber link.
Since the aforementioned forward power control performance is known to be different in accordance with the associated parameter, optimal parameters are used for actual system performance test. However, optimal parameters must be defined with respect to some defined criteria. For example, if tracking error is selected as the criteria to judge forward power control performance, then the parameter confirmation which gives the best results for forward power control based on tracking error is selected as optimal.
There exists a need, therefore, for a simple and effective method for optimizing forward power control. Until now, tracking error has not been considered as a criterion for meeting the objectives of optimizing forward power control.
It is an object of the present invention to provide a system and method for optimizing forward power control parameters simply and effectively using tracking error as a criterion for evaluating forward power control performance in a PCS CDMA system.
Definitions
Channel change: A channel signal from a base transceiver station is changing due to interference, noise and shadowing in a radio environment. The present invention simulates a channel change in a live radio environment by artificially manipulating a sinusoid.
According to one embodiment of the present invention, a laboratory test method for determining parameters optimizing the forward power control in a PCS CDMA system comprises the steps of: establishing a laboratory test environment to simulate noise and fading effects on a channel change, which occurs in a live radio environment, by manipulating the frequency and the amplitude of a laboratory generated sinusoid, determining an amplitude value and cycle value of the channel change such that the pilot signal strength (i.e., the ratio of energy per chip to noise)       E    c        I    O  
of a mobile station changes within a predetermined limit, setting forward parameter values for a plurality of parameter combinations by a base station manager (BSM), making a test call in accordance with switched virtual circuit option 9 (loop call), starting data logging by a data collection platform(DCP) and a mobile diagnostic monitor (MDM), terminating data logging after a predetermined time period, and storing the collected data.
According to an alternative embodiment of the present invention, a method for determining parameters to optimize the forward power control in a PCS CDMA system comprises the steps of: making channel changes by manipulating the frequency and amplitude of a sinusoid to simulate noise and shadowing, calculating a forward frame error rate, reverse frame error rate, average             E      c              I      O        ,
and average digital gain of data per combination of forward parameters, calculating a tracking error per combination of forward parameters, and determining optimal parameters by which the frame error rate is maintained at a predetermined value, such that the average digital gain is low and the tracking error is at its lowest.